app/controllers/stream_notifications_controller.rb

@@ -16,8 +16,7 @@ class StreamNotificationsController < ApplicationController
       notify_users
     when "video.asset.ready"
       full_live_stream_playback_uid = notification.dig(:data, :playback_ids, 0, :id)
-      @broadcast.full_live_stream_playback_uid = full_live_stream_playback_uid
-      @broadcast.save
+      @broadcast.update(full_live_stream_playback_uid: full_live_stream_playback_uid)
       notify_users
     when "video.live_stream.active"
       @broadcast.active!

app/models/broadcast.rb

@@ -31,6 +31,8 @@ class Broadcast < ApplicationRecord
   end
 
   def full_live_stream_playback_url
+    return stream_playback_url if full_live_stream_playback_uid.blank?
+
     "https://stream.mux.com/#{full_live_stream_playback_uid}.m3u8"
   end